Sayyiduna al-Bara' (may Allah be pleased with him) said: "I and Ibn Umar were presented before the Prophet (peace and blessings be upon him) on the day of Badr, and we were considered too young (and were not permitted), and we took part in Uhud."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1155